NONE
The present invention generally relates to a thermal ink jet printer ink. More specifically, the present invention relates to a thermal ink jet printer ink that may incorporate a pigment dispersion. The present invention further relates to a pigmented, thermal ink jet printer ink with a long shelf life.
Thermal ink jet printing is a commonly used method of recording images on recording material, such as paper or cloth, by discharging discrete droplets of ink from nozzles of a print head and allowing these droplets to be absorbed by the recording material. Thermal ink jet recording offers opportunities for quiet, high speed, full color printing. Also, images printed with thermal ink jet printers seldom need to be fixed or treated after the ink droplets are absorbed on the recording material.
Thermal ink-jet printing is a non-impact printing process in which ink droplets are formed and thereafter deposited on a print medium in a particular order to form an image on the print medium. The low cost and high quality of the printed output in combination with the relatively noise-free operation of ink jet printers have made ink jet printing a popular and economical alternative to other types of printing in consumer, office, and industrial settings.
Thermal ink-jet printing is one example of a drop-on-demand form of non-impact printing. Other examples of drop-on-demand systems, besides thermal ink jet, are piezoelectric ink jet, acoustic ink jet, and vibrating ink jet systems. Besides drop-on-demand systems, there are also continuous stream ink jet printing systems. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The steam of ink is then broken up into droplets at a fixed distance from the orifice, and the ink droplets are thereafter directed toward the recording medium or recycled into the printing ink supply.
In drop-on-demand systems, an ink droplet is not formed or expelled from the print head unless the droplet is to be placed on the recording medium. Therefore, since drop-on-demand systems require no ink recovery or post-ejection treatment, drop-on-demand systems are typically somewhat simpler in construction and operation than continuous stream ink jet printing systems. Thermal ink jet (sometimes referred to as xe2x80x9cbubble jetxe2x80x9d) systems are one of the most common types of drop-on-demand ink jet printing systems.
In thermal ink jet printing, the energy for drop formation and ejection is generated by electrically heated resistor elements. The resistor elements heat up rapidly in response to electrical signals from a microprocessor to create a vapor bubble. Superheating of the ink far above the normal boiling point of the ink causes the bubble formation. The expansion of the bubble forces a droplet of ink out of a nozzle at a high rate of speed toward the recording medium. After the collapse of the bubble, the ink channel proximate the resistor element refills by capillary action.
Colorants for inks printed by thermal ink jet printing may be generally classified as dyes or pigments. Accordingly, thermal ink jet printer inks may incorporate dye(s), pigment(s), or a combination of dye(s) and pigment(s) to print images on the recording media. Of these three, dye-based thermal ink jet printer ink compositions are most widely available commercially.
One reason that dyes are sometimes selected over pigments concerns the expansive color gamuts and color vibrancy that combinations of different, separately-applied, dye-based thermal ink jet inks typically achieve via process printing, as compared to combinations of conventional pigment-based inks that are separately applied via process printing. Also, the mechanics of printing dye-based inks via thermal ink jet are often simpler than those of printing pigment-based inks since pigments often constitute relatively large particles, as opposed to the molecules of dyes. These particles of pigment may influence the mechanism of drop formation and consequently may enhance the difficulty of achieving good printing performance, such as optimum drop size (drop volume), velocity, and trajectory, as compared to thermal ink jet inks that are based upon molecule-size dyes. Finally, owing to the particle form of pigments, there is a tendency for the pigments of pigmented inks, such as thermal ink jet ink, to sediment, agglomerate, and/or flocculate if the pigments are not properly dispersed in the suspension medium of the ink over the long term. Dyes, as compared to pigments, do not typically exhibit this tendency toward sedimentation, agglomeration, and/or flocculation since dyes are typically in the form of molecules, as opposed to particles.
However, despite these advantages of dye-based inks, there is motivation to use pigments instead of dyes in printing inks. For example, pigments typically exhibit enhanced light fastness characteristics, as compared to dyes. More specifically, printed images formed from thermal ink jet printing inks are often more resistant to color degradation and fading upon exposure to various types of light, such as ultraviolet light, as compared to dyes. Also, pigment-based inks are typically more water resistant than dye-based inks, since many dyes are water soluble to some extent. Furthermore, in many potential new markets for thermal ink jet printing, pigment has traditionally been used as the colorant in printing inks. For example, in the graphic arts industry, the printing systems that are predominantly relied upon, such as lithographic printing, screen printing, gravure printing, flexographic printing, and offset printing, typically employ pigmented inks, as opposed to dye-based inks. Consequently, due to the familiarity of these potential new markets with pigmented inks, any attempt to penetrate these new markets with thermal ink jet printing would benefit from incorporating pigmented ink.
Much development work has focused on pigmented thermal ink jet inks over the past decade or so. Many approaches have focused on preparation of thermal ink jet inks using increasingly sophisticated proprietary pigments. Other attempts have been made to enhance dispersion of pigments in ink using increasingly sophisticated compounds. Though these attempts have added to the store of knowledge concerning pigmented thermal ink jet inks, problems still remain. For example, despite these attempts to enhance dispersion of pigments in ink, no one has found an inexpensive way to maintain uniform dispersion of pigments in thermal ink jet inks over longer periods of time, such as about a month, about six months, about one year, or even about two years or longer. Indeed, pigment particle settling, agglomeration, and/or flocculation, within as little as a few hours or days of manufacture, are prevalent among commercially available pigmented thermal ink jet inks, including even expensive pigmented thermal ink jet inks that are based upon sophisticated proprietary pigments and/or sophisticated dispersion agents.
Corresponding to the increasingly sophisticated and propriety nature of pigments and pigment dispersants, the cost of preparing pigment-based thermal ink jet printer ink has skyrocketed. These sophisticated pigments and pigment dispersants are only available at a high cost, due to the research and development costs that led to creation of these sophisticated pigments and pigment dispersants and/or due to the costly processing and/or mechanical equipment required to prepare these sophisticated pigments and pigment dispersants. Consequently, retail purchase prices for pigmented thermal ink jet inks are often as high as about $300 per pound, or more, depending upon the sophistication of the pigment and pigment dispersant.
On the other hand, in the graphic arts industry, retail purchase prices for inks used in lithographic printing, screen printing, gravure printing, flexographic printing, and offset printing typically are as low as about $5 per pound, or less. Thus, retail purchase prices for prior pigmented thermal ink jet inks are as much as about 60 times greater than the retail purchase prices for inks currently used in the graphic arts industry. Clearly, despite any cost advantages of thermal ink jet printing equipment itself, the cost of pigmented thermal ink jet ink will need to drop dramatically before new markets for thermal ink jet printing, such as the graphic arts industry, show much interest in thermal ink jet printing.
Though pigmented thermal ink jet inks should include pigment particles that remain uniformly dispersed in the ink for longer periods of time, such as a month, a year, or even two years or longer, such stability conflicts with other desirable properties of pigmented thermal ink jet inks. For example, pigmented thermal ink jet ink will preferably be capable of easy application to the recording media as small, discrete droplets that are capable of bonding to the recording media as uniform dots. Should a uniform and stable dispersion of the pigment in the pigmented thermal ink jet ink exist, interaction of properties of the pigment with properties of the dispersion medium of the ink will be responsible for the uniform and stable dispersion of the pigment in the pigmented thermal ink jet ink.
However, by virtue of heating the pigmented thermal ink jet ink with the resistor elements and subsequently ejecting the heated pigmented thermal ink jet ink from the printer nozzle, some of the dispersion medium of the ink will be evaporated during the thermal ink jet printing process. More of the dispersion medium will typically be evaporated from the pigmented thermal ink jet ink as droplets of the pigmented thermal ink jet ink contact and bond with the recording medium. Thus, during the printing process, the interaction of properties of the pigment with properties of the dispersion medium of the ink that are responsible for the uniform and stable dispersion of the pigment in the pigmented thermal ink jet ink will be disturbed, which would be expected to diminish, or even destroy, the uniform distribution of the pigment in the printed droplets of the ink, and consequently the formation of uniform ink dots on the recording media.
Thus, what is needed to maintain the uniform and stable dispersion of the pigment in the pigmented thermal ink jet ink (i.e.: the interaction of properties of the pigment with properties of the dispersion medium of the ink) prior to printing would be expected to hinder formation of uniform ink dots and uniform distribution of pigment in the printed ink dots. Consequently, these competing variables of uniform and stable dispersion of the pigment in the pigmented thermal ink jet ink along with formation of uniform ink dots and uniform distribution of pigment in the printed ink dots are inherently inconsistent with each other and present complex competing variable problems.
Dyes have also enjoyed an advantage over pigments due to the ability of a particular dye set with a predetermined number of dyes to often attain a greater percentage of a particular color gamut than a particular pigment set with the same predetermined number of pigments. One particular color gamut of interest is the color gamut of the PANTONE MATCHING SYSTEM(copyright) color matching system. The PANTONE MATCHING SYSTEM(copyright) color matching system is one of the most popular color matching systems in the printing industry, especially in the United States.
Traditionally, the printing industry has relied upon a set of inks in different colors that are applied by process printing. The process printing ink sets may have been based upon inks that included dyes, pigments, or a combination of dyes and pigments. An image created using process printing will typically not exactly match a targeted color from the color gamut of the PANTONE MATCHING SYSTEM(copyright) color matching system because of differences between process printing and the method of printing used to define the color gamut of the PANTONE MATCHING SYSTEM(copyright) color matching system. Specifically, the color gamut of the PANTONE MATCHING SYSTEM(copyright) color matching system is based upon spot coloring which entails mixing combinations of different colored inks to form a single ink of a particular color that is thereafter applied to a recording medium to characterize one discrete color of the color gamut. Spot coloring of additional single color inks based upon different combinations of different colored inks proceeds to fill out and define the color gamut of the PANTONE MATCHING SYSTEM(copyright) color matching system. On the other hand, in process printing, the different colored inks of the ink sets are applied individually, by process printing, as subtractive color layers on the recording medium, instead of mixing the different colored inks prior to application to the recording medium.
This difference in application technique between process printing (applying different colored inks separately) versus spot coloring (mixing different colored inks prior to application) typically prevents process printing from exactly matching a predetermined, particular color from a particular color gamut, such as the color gamut of the PANTONE MATCHING SYSTEM(copyright) color matching system. Also, due to a variety of factors, such as differing ink absorbencies between different substrates, differing interactions of the same inks between different substrates, and non-uniformities of the same ink between applications to different substrates, inks applied by process printing that seemingly should have the same color actually exhibit a different color depending upon which substrate the ink is applied to. Furthermore, due to the aforementioned ink non-uniformities, process printing of the same ink to identical copies of the same substrate at different times often causes the printed ink to exhibit different colors on the identical copies of the same substrate. Nonetheless, process printing offers advantages over spot coloring, since spot coloring has traditionally been prohibitively expensive for printing jobs where the printed image will need to exhibit more than about one to three different colors.
Traditionally, four-color process printing (sometimes referred to as CMYK printing) that relies upon a cyan-colored ink, a magenta-colored ink, a yellow-colored ink, and a black ink has been the most common form of process printing. One example of a commercially available four-color process printing model that relies upon pigment-based inks is the PANTONE(copyright) process color model. However, the PANTONE(copyright) process color model suffers from a major drawback.
Specifically, the PANTONE(copyright) process color model is only capable of attaining about 50% of the color gamut of the PANTONE MATCHING SYSTEM(copyright) color matching system. An evolution from four-color process printing is six-color process printing which relies upon six different process colors, rather than four different process colors. One example of a commercially available six-color process printing model that relies upon pigment-based inks is the PANTONE HEXACHROME(copyright) process color model. While the six-color PANTONE HEXACHROME(copyright) process color model does represent an improvement over the four-color PANTONE(copyright) process color model, the six-color PANTONE HEXACHROME(copyright) process color model is still only able to attain about 90% of the color gamut of the PANTONE MATCHING SYSTEM(copyright) color matching system. Furthermore, both the four color PANTONE(copyright) process color model and the six color PANTONE HEXACHROME(copyright) process color model suffer from the dual shortcomings of poor color repeatability when printed on different substrates and poor color repeatability when printed at different times on identical copies of the same substrate.
A need exists for a pigmented thermal ink jet printing ink that may be incorporated, in different colors, as part of a set of different colored printing inks for process printing. Pigmented inks offer definite advantages over dye-based inks, such as superior light fastness and superior water resistance. Furthermore, the graphic arts industry traditionally relies upon pigmented inks. However, since the graphic arts industry relies upon printing techniques that are more cumbersome and less efficient than thermal ink jet printing, an advance in pigmented thermal ink jet printing ink is needed that will encourage the graphic arts industry to embrace thermal ink jet printing while retaining the noted benefits of pigmented inks.
First, the complexity and cost of manufacturing pigmented thermal ink jet printing inks must be reduced to be more in line with the cost of printing inks traditionally used in the graphic arts industry. Also, pigmented thermal ink jet printing inks must be made more stable against sedimentation, agglomeration, and/or flocculation while retaining good drop formation attributes and good printing characteristics. Finally, a system of printing with pigmented thermal inkjet printing inks is needed that repeatably attains color gamuts, such as the color gamut of the PANTONE MATCHING SYSTEM(copyright) color matching system, no matter the substrate and no matter when the printing occurs. These requirements are met by the pigmented thermal ink jet printing inks of the present invention and the system of the present invention that employs sets of the inventive pigmented thermal ink jet printing inks for thermal ink jet printing.
The present invention includes a method of making an ink jet ink The method entails combining a water miscible organic solvent, water, and a pigment dispersion, and blending the water miscible organic solvent, the water, and the pigment dispersion together to form the ink jet ink. The ink jet ink produced by this method is capable of exhibiting no pigment precipitation, no pigment agglomeration, and no pigment flocculation after being stored in the absence of any agitation for a period of at least about 1 month. The present invention further includes a method of forming a printed image on a recording medium and a thermal ink jet ink.